Transcript for How police say Scott Peterson reacted to wife's disappearance: Part 1
A pregnant young wan gone missing. Laura wallens' loved ones tearfully asking for her return. There's so many people, so many people that miss you, who are praying that you're safe. Reporter: This was the scene last week in Maryland as the missing woman's boyfriend, Tyler Tessier, held her mother's hand. But if this story reminded you of another case of a missing pregnant woman, the possible parallels are about to intensefy. The Maryland man arraigned on murder charges in the death of his girlfriend -- Reporter: Tyler Tessier was charged with murder on Wednesday. His lawyer had no comment. But the earlier case of Scott Peterson and the disappearance of his beautiful wife Laci continues to haunt us to this day. December 24th, 2002. Hi, can I help you? Yes, my daughter has been missing since this morning. She's eight months pregnant. She took her dog for a walk in the park. Reporter: Laci Peterson, 27 years old, 7 1/2 months pregnant, goes missing on Christmas eve, making national news headlines. A California man is anxiously waiting to hear word on the mysterious Christmas eve disappearance of his pregnant wife. She's considered a high-risk missing person under suspicious circumstances. Laci was last seen by her husband Scott. Reporter: The community quickly mobilizes, making flyers and searching for Laci. Please bring her back to us. Please. Reporter: Laci Peterson and her husband Scott Peterson had been married just a few years. They were expecting the birth of their first child. But Scott quickly becomes a person of interest in the disappearance of his wife. The first person you focus at in a homicide investigation is the person closest to the victim. Scott Peterson says that Laci went to walk their dog Mckenzie. Scott finished fishing that day at some point in the afternoon. And made a phone call to Laci. Hey, beautiful. I won't be able to get to villa farms to get that basket for papa. I was hoping you would get this message and go on out there. I'll see you in a bit, sweetie, about. Ye. Scott Peterson says he came back home from his fishing trip, minus the fish. And comes in, Laci! No Laci. So what does he do? He goes over to the washing machine, takes all the clothes out, takes all his clothes off and washes them. Then he gets some pizza out. He drinks some milk and eats some pizza. He goes and takes a shower. And then he calls Sharon and says, Laci's missing. I remember running around in the park and yelling her name. There's nothing worse than lifting up a trash can, looking for your child to see if her body is in a trash can. I remember doing that. Reporter: Laci had seemingly disappeared without a trace. We didn't find any fingerprints that were present in the house that didn't belong there. There was nothing that was missing from the house. TV was still there. All the Normal things that burglars will take quickly, so they can get out of there. So what scenario does that leave? I suspected Scott when I first met him. Didn't mean he did it, but I was a little bit thrown off by his calm, cool demeanor. Reporter: Police decide to bring in Scott for questioning, seen here in this interrogation video. So today, she told you what she was going to do for the day. Yeah. And what was that? Take the dog for a walk. And then she was going to the store to buy for Christmas morning breakfast tomorrow. She was going to make gingerbread cookies for tonight. He didn't have that sense of urgency that you would expect, that you saw from other people. Have you guys -- you guys haven't had any problems, marriage problems? No. Everything's good? Uh-huh. You been married four years? Yeah. He just doesn't seem like the guy whose wife is missing. Reporter: While Scott seems cool, calm and collected, Laci's parents make an emotional plea for their daughter's safe return. Whoever has her, please, please, please let her go. Bring her back to us. We love her so much. We want her back. Please. Let us have her back. Scott was always in the background, he always gave the excuse he didn't want it to be about him, he wanted the focus to be on Laci. If your wife or husband or baby were missing, what would you do? To find them? How far would you go? To the end of the effort? Earth? To the local TV station? Who wouldn't? Scott Peterson. It's our thoughts that if I was to hold back from the media, the media would continue to come. Because frankly, cameras, reporters, they want something they can't get right away. This was our way of keeping the media coming back for it. Reporter: Days pass and still no Laci. So police decide to expand their search to the water. We believe she was in the bay. So we're searching the bay. What's he doing? He's renting cars, driving to the bay. Just to see where we're looking, to see where the boats are. He isn't checking in with us to say, hey, how's the search going? Is it possible they think you know where she is? I think a lot of people believe that. Are you afraid police will arrest you? No. I know there's no basis. I had nothing to do with her disappearance. So there's no possible evidence or anything like that. I mean, it's not like this is a total stranger that you might be suspecting. Because I knew in my heart that if he did, she wasn't coming home. Reporter: That night the family holds a candlelight vigil for Laci. Just keep looking for Laci. Please don't give up. They ask about the candlelight vigil that we held in the park. They asked, why weren't you on that stage with the family? Frankly, because this isn't about us, to be out in front of the camera. It's about us to work toward bringing home one person that's hurting the most. The piece of our family that's missing right now. Reporter: Unbeknost to everyone, while at that vigil, Scott places a call to another woman. Amber Frey. I met Scott Peterson November 20th, 2002. Scott told me he was not married. We did have a romantic relationship. Amber Frey had contacted Modesto police department on Monday, December 30th, 2002. She met with detectives and gave the information about the relationship with Scott Peterson. And amber Frey has been eliminated as a suspect in Laci Peterson's disappearance. He was good-looking, he was nice, he was funny. Attendive to me. I really liked him. And felt really good about where things were going. And our conversations and time spent together. Amber Frey was not his first lover outside the marriage. Okay? I mean, that's a given. The only thing that had changed is that Laci got pregnant. I remembered asking him if he'd ever been married. He said no. But that wasn't true, of course. And as it turns out, amber's friend, who introduced her to Scott, found out that he was married and confronted him and said, if you don't tell amber, I will. Reporter: However, in early December, Scott Peterson does come clean. Sort of. He tells amber that he is married but implies that his wife has died. And just weeks later his wife would actually go missing. Amber Frey started cooperating with police as soon as she learned that the man of her dreams was really a married man whose wife had disappeared, and he had been lying to her all along. I buy her a tape recorder with some cassette tapes and a wire that can hook onto her phone. And I tell her, okay, if he ever calls, just push these two buttons and just talk Normal. The phone rings. And it's Scott Peterson. I'm like, that's him. Showtime, girl. Hey, happy new year's. Happy new year's. What they heard onecember 31st, 2002, was a Scott Peterson who, while a candlelight vigil is being held for his missing wife and he's attending it, is also on the phone with amber Frey, being recorded unbeknownst to him, telling her that he's in Europe. I'm near the eiffel tower. New year's, it's unreal. The crowd, it's huge. The crowd's huge? He was right down the street. Where the vigil was taking place. Okay? Now the motive not only becomes clear, it's personified. There she is. He killed Laci to be with this woman. Instantly, as soon as amber Frey showed up, people are like, he's guilty. He now is enemy number one. Everybody hates Scott Peterson. Scott, why don't you answer some questions? Did you murder your wife? Stay with us.
This transcript has been automatically generated and may not be 100% accurate.